X-ray computed tomography (CT), which is widely used clinically, does not make full use of the spectral dependence of X-ray attenuation in tissues and contrast agents, and for that reason it delivers sub-optimal images at greater than necessary dose to the patient. CT alone contributes almost half the total radiation exposure for medical use in the US, and one quarter of the total radiation exposure per capita. This is a huge source of potential risk for radiation-induced malignancy, with one study suggesting that more than one percent of cancers may eventually be caused by the radiation currently used in CT. We propose a new Spectral CT technology with important application to CT dose reduction. Dual-energy CT (DECT) makes some use of X-ray spectral information, but it is limited in the materials it can distinguish within a single imaging session, has inadequate quantitative accuracy, and delivers higher dose than is necessary. Multiple energy or Spectral CT (SCT) has been explored with energy-resolved single- photon counting detectors, but these are expensive and are currently incapable of accurate operation in clinical CT X-ray fluxes due to rate limitations. The lack of a rate-capable, accurate, and cost-effective Spectral CT is currently limiting the contrast and quantitative accuracy of clinical CT images while simultaneously elevating the patient dose needed to obtain these images, and is holding back progress on the development of the next generation of CT contrast agents. We propose a novel CT system design that will improve image accuracy and reduce patient dose relative to DECT, will build on the clinical advantages of DECT relative to single-energy CT, and will enable new clinical applications by making practical, cost-effective, and accurate SCT available at clinically relevant X-ray flux rates. In preliminary investigations, we have performed the first measurements of this new design by modifying the CT component of a PET/CT system which we currently manufacture. In our proposed Phase I effort, we will accomplish a proof-of-concept demonstration of the performance improvements and dose reductions obtainable with our design by performing a series of measurements on standardized test objects using our current prototype. In a later Phase II effort, we will develop and test an engineering prototype with which we will demonstrate the manufacturing feasibility and performance capability of a clinical CT system incorporating our new design.